It is common practice in the medicinal industry to store a medicine, such as a drug solution, in a vial under a sealed condition till the time of administration to patients. Where it is required that the guaranteed shelf life of the drug solution should be prolonged, the drug solution is freeze-dried within a vial, and the thus obtained freeze-dried formulation is stored in the sealed vial, and then returned to a liquid state by adding a diluent or a solvent at the time of administration to a patient. The drug solution may be stored in a vial without being freeze-dried. A solid drug, such as powder produced in advance, may also be stored in a vial. Hereinafter, a drug solution, freeze-dried formulation, a solid drug, and the like are generally called drugs.
The common vial available in the market has a closed-end cylindrical body (barrel) for containing a drug, and a contracted mouth to define an upper opening of the body, wherein a radially projected flange is formed on the outer periphery of the upper end of the mouth. A rubber stopper is fitted into the mouth of the vial to seal the drug therein, and then this rubber stopper is fixed onto the flange of the vial with a thin aluminum cap wound tightly thereon to ensure that the rubber stopper will not be removed till the time of administration of the drug.
However, some problems are inherent in the use of the aluminum cap. One of them is that the sharp edge generated in removing the cap may possibly damage the latex gloves worn by health care professionals. The other is that, when the aluminum cap is torn, metal particles may be caused and mixed into the drug. Also, the separation of combustibles from incombustibles is required for disposal from a view point of environmental protection in recent years, however, it is practically difficult to sort out only aluminum caps for disposal on the medical treatment front.
In order to solve these problems, the applicant of the present invention has developed plastic snap-on caps for vials heretofore and, for example, discloses the following Patent Literature 1 and 2.
These snap-on caps each have a cylindrical cap body and a protective cover, made each of a synthetic resin, the cap body attached to surround a mouth of a vial and provided with a through hole in the central part thereof, and the protective cover attached to the upper surface of the cap body to close the through hole for preventing a rubber stopper from being contaminated via the through hole during storage. The protective cover is formed, separately from the cap body, and is attached to the cap body.